[Lens] No indication when date histogram can not use the specified custom interval

[tsullivan]

Kibana version: 7.14.0-bc2
Describe the bug: When editing a Lens with a date histogram, such as a table or a bar chart, the user is given an option to customize the date interval. However, certain inputs for the custom interval do not work, and no indication is given why.

Steps to reproduce:

1. Create a Lens data table with a date histogram showing 300 or so rows for a daily interval.
   
2. Change the interval from 1 days to 24 hours this seems to be fine, but the hours are not showing in the date format.
3. Lower the number of hours. This erroneously makes the table aggregated by a daily interval.

Expected behavior:
It should be possible to aggregate the date histogram by < 1 day intervals, but it is not.

Screenshots (if relevant):

no-hourly-2021-07-08_22.22.39.mp4

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[flash1293]

Closing as this works as expected - the specified interval is a "minimum interval" as it says in the UI and is subject to be scaled up to match the maximum allowed buckets configured in advanced settings. I'm closing this in favor of #75198 which is tracking a similar thing and left a note there.